Old fish, new genes

Thought to be extinct for 65 million years, a surprise coelacanth (pronounced see-luh-kanth) was captured in 1938 and dubbed a “living fossil”. But while this old fish might look like a fossil, it has a few genes from a strange place.

A team of researchers led by Isaac Yellan of the University of Toronto, Canada, have found that the African coelacanth, Latimeria chalumnae, gained 62 new genes from random encounters with other species around 10 million years ago.

Interestingly, these new DNA sequences came from transposons, which are a DNA element that can “jump” around the genome – hence, “jumping genes”.

In this case, the transposons leaped from one species to the coelacanth, where it became ingrained in the coelacanth’s genome, the authors report in their paper, published in Molecular Biology and Evolution.

“It was surprising to see coelacanths pop out among vertebrates as having a really large number of these transposon-derived genes because they have an undeserved reputation of being a living fossil,” says Yellan.

“The coelacanth may have evolved a bit more slowly but it is certainly not a fossil.”

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Key research points

• The coelacanth has 62 genes gained from other species
• Genes were transferred between species as parasitic “jumping genes”
• The genes found were related to human CGGBP1
• They may have a role in DNA expression

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Yellan was looking for genes related to the human gene, CGGBP1. It’s  common in many mammals, birds and reptiles, but the gene ancestry doesn’t match normal gene inheritance. It’s found in many unrelated species, even in moss, but sometimes not in closely related ones.

This patchy representation across species probably happened because of horizontal gene transfer, the authors report. This happens when those transposable genes spread by “copy and pasting” themselves into other species, so that the pattern of inheritance is completely different from a normal family tree.

This doesn’t require sexual reproduction, but instead acts like a DNA parasite, which is why the genes can jump between very different species. It’s somewhat like trying to trace where a family heirloom has come from, but you discover that people were making copies and sharing it with strangers instead of kin.

“Horizontal gene transfer fuzzies up the picture of where the transposons came from, but we know from other species that it can occur via parasitism,” says Yellan. “The most likely explanation is that they were introduced multiple times throughout evolutionary history.”

“Our findings provide a rather striking example of this phenomenon of transposons contributing to the host genome,” says Tim Hughes, senior author on the study.

“We don’t know what these 62 genes are doing, but many of them encode DNA binding proteins and probably have a role in gene regulation, where even subtle changes are important in evolution.”

As to where these genes came from, that may remain a mystery unless some lucky fisher pulls up another fossil with intact DNA.

“The coelacanths are extremely rare,” says Yellan. “And they’re very good at hiding.”